This Problem Set is a part of the Lesson 2, Unit 5, Grade 8. In this second introductory lesson, students learn the term function for a rule that produces a single output for a given input. Understand that a rule that produces exactly one output for each allowable input defines the output as a function of the input. Learning targets: students know that a function is a rule with exactly one output for each allowable input and that if a rule has exactly one output for each allowable input, then the output depends on the input.